The XChangePointerDevice
request causes the server to use the specified device as the X pointer.
The device must have been opened by the client via XOpenDevice or a BadDevice
error will result. The device must support input class Valuators or a BadMatch
error will result. If the implementation does not support use of the specified
device as the X pointer, a BadDevice error will result.

If the specified
device is grabbed by another client, AlreadyGrabbed is returned. If the
specified device is frozen by a grab on another device, GrabFrozen is returned.
If the request is successful, Success is returned.

If the request succeeds,
a ChangeDeviceNotify event is sent to all clients that have selected that
event. A MappingNotify event with request = MappingPointer is sent to all
clients. The specified device becomes the X pointer, and the old X pointer
becomes accessible through the input extension protocol requests.

An invalid
device was specified. The specified device does not exist, has not been
opened by this client via XOpenInputDevice, or is already one of the core
X input devices (pointer or keyboard). This error may also occur if the
server implementation does not support using the specified device as the
X pointer.

BadMatch

This error may occur if an XChangePointerDevice request
was made specifying a device that has less than two valuators, or specifying
a valuator index beyond the range supported by the device.